How do I test my pH electrode?
- Set the pH/mV switch on the pH meter to the mV position.
- Connect a shorting plug to the input on the pH meter, or connect a precision mV generator with a 0 mV input.
- Disconnect the shorting plug/precision mV generator, and connect the electrode that will be tested.
By using a standardized buffer that has well-defined characteristics and testing it against your pH meter, your meter will adjust automatically. Failure to calibrate pH meters and probes can skew your readings and damage your equipment.
After opening, a bottle of 4 or 7 buffer solution should last approximately 3 to 6 months and a bottle of pH 10 buffer should last approximately one month.
- Remove the protective cap from the handheld pH meter. Put the composite electrode into distilled water, and slowly stir it for 5-10 seconds, then take out the pH meter and spin-dry it.
- Press the ON/OFF button to turn on the unit.
- Stir the solution gently and wait for the value to stabilize.
Pure water has a neutral pH of 7. pH values lower than 7 are acidic, and pH values higher than 7 are alkaline (basic).
What does it mean for a solution to be acidic or basic (alkaline)?
| pH Value | H+ Concentration Relative to Pure Water | Example |
|---|
| 10 | 0.001 | Great Salt Lake, milk of magnesia |
General Cleaning: Soak the electrode in 1:10 dilution of household laundry bleach in a 0.1 to 0.5% liquid detergent solution in hot water with vigorous stirring for 15 minutes. Place junction under warm, running tap water for 15 seconds. Drain/refill the reference chamber.
The pH meter has a finite life due to the gradual aging of the sensor and will only last for approximately 360 readings (or a year for one reading a day).
Most manufacturers of pH electrodes build to a quality level that gives an accuracy of approximately 0.1 pH. If the pH sensor is properly maintained, calibrations done correctly, and stored according to manufacturer recommendations, then 0.1 is possible.
** Before you begin, please ensure you have a container of water to rinse the probe between the 2 buffer solutions during the calibration. If you have Deionized water, Distilled water or RO water (Reverse Osmosis) – any of these are preferred to tap water, however you may use tap water if necessary.
Keeping your pH measurements reliable and accurate.
- Always read the manual. Calibration procedures change based on which meter is used.
- Ensure your calibration points bracket the pH range of your sample.
- Use best practices.
- Calibrate often.
- Be aware of your offset and slope.
- Electrode care.
- Keep a record of calibrations.
pH testers that have been designed for the garden are not very accurate, as has been discussed in Soil pH Testers – Are They Accurate? If you really want to know the accurate pH of your soil have it tested by a professional lab. Their meters work and are accurate.
Place the electrode in the correct buffer solution and press measure to take the reading. Rinse and dry the electrode well. Now, place the electrode in the sample, press the measure button, and keep it for about two minutes. This is your pH reading.
The pH meter measures the difference in electrical potential between a pH electrode and a reference electrode, and so the pH meter is sometimes referred to as a "potentiometric pH meter".
If pH readings become unstable or erratic, the electrode should be cleaned and then rehydrated. Soak the electrode in electrode storage solution for at least one hour to rehydrate it. In some cases, it may be necessary to soak the electrode overnight.
Normal saline and distilled water had pH of 5.4 and 5.7, respectively. Facial mineral water had pH between 7.5 and 8, while facial makeup removing water had an acidic pH.
Broken electrode – The pH meter will display the same value when placed in different buffers or samples. This indicates a crack or break in the sensing glass. Change the fill solution, clean, condition, and calibrate the electrode, if this does not improve the slope, replace the electrode.
Other possible explanations of fluctuating pH measurements include: The electrode tips are insufficiently or not continuously immersed in the solution. In this case increase the measuring volume. The glass pH electrode was stored incorrectly and is not functioning correctly.
Which of the following is not a failure in pH meters? Explanation: Defective calibration is not a failure in pH meters. Failure occurs due to defective electrodes, defective input circuitry and defective electronic circuitry.
A key component of the glass combination electrode's reference system is the reference electrolyte. Over time, the measured solution will often work its way through the liquid junction and contaminate the reference electrolyte. This contamination can shift the electrode's zero-point and lead to pH measurement drift.
Buffer solutions are used to calibrate pH meters because they resist changes in pH. When you use a pH meter to measure pH, you want to be sure that if the meter says pH = 7.00, the pH really is 7.00. They resist changes in pH if you accidentally add a little acid or base or even water.
What Variables Affect pH Levels?
- Carbon Dioxide. When dissolved in water, carbon dioxide forms a weak acid that can throw off the balance of the pH.
- Acidics and Akalines.
- Sodium and Calcium Hypochlorite.
- Chlorine.
- Air-borne Contaminants.
- Air Pollution.
4 Factors that Affect PH
- CO2 Concentration in Water. The concentration of carbon dioxide (CO2) dissolved in water becomes a factor that affects pH.
- Temperature.
- Carbonate and Bicarbonate Concentrations.
- Organic Material Decomposition Process.
In basic solutions, the pH value increases with increasing pressure (e.g. NH3 in water) and in acidic solutions it decreases (e.g. SO2 in water). If a reference measurement is made under normal pressure conditions, the measurement result will be correspondingly higher or lower.
Because the resolution forms the upper limit of precision, low-resolution measurement techniques such as test strips have less potential to be precise compared with higher resolution techniques such as pH meters. In summary, pH meters are usually much more precise and accurate than test strips.
*pH decreases with increase in temperature. In the case of pure water, there are always the same concentration of hydrogen ions and hydroxide ions and hence, the water is still neutral (even if its pH changes). At 100°C, a pH value of 6.14 is the New neutral point on the pH scale at this higher temperature. 
